[英]Postgres inheritance with SQLAlchemy
我有一個關於使用SQLAlchemy制作PostgreSQL表繼承的問題。
我有這兩個表:
CREATE TABLE his
(
idg integer,
idfk integer,
idh integer NOT NULL defautl nextval('his_seq'),
"type" character varying,
CONSTRAINT __his_pkey PRIMARY KEY (idh)
);
CREATE TABLE data
(
"text" character varying,
)
INHERITS (his);
在執行任何ddl命令之前,我已經創建了這個python代碼:
from sqlalchemy import *
from sqlalchemy.orm import Session
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import event
Base = declarative_base()
class His(Base):
__tablename__ = 'his'
idg = Column(Integer())
idfk = Column(Integer())
idh = Column(Integer(), Sequence('his_seq', start=1, increment=1), primary_key=True)
type= Column(String())
__mapper_args__ = {'polymorphic_on': type}
__table_args__ = {'implicit_returning':False}
def __init__(self, idg, idfk, type):
self.idg = idg
self.idfk = idfk
self.type = type
class Data(His):
__tablename__ = None
# __mapper_args__ = {'polymorphic_identity': 'data', 'concrete':True}
__mapper_args__ = {'polymorphic_identity': 'data'}
text = Column(String())
def __init__(self, text):
self.text = text
@event.listens_for(His.__table__, 'after_create')
def create_child_tables(target, connection, **kw):
connection.execute("""
CREATE TABLE data(
) INHERITS (his)
""")
connection.execute("""
CREATE OR REPLACE FUNCTION his_insert_trigger()
RETURNS TRIGGER AS $$
BEGIN
IF (NEW.type='data') THEN
INSERT INTO data VALUES (NEW.*);
ELSE
RAISE EXCEPTION 'Table type is unknown for historical porpurses.';
END IF;
RETURN NULL;
END;
$$
LANGUAGE plpgsql;
""")
connection.execute("""
CREATE TRIGGER his_insert
BEFORE INSERT ON his
FOR EACH ROW EXECUTE PROCEDURE his_insert_trigger();
""")
@event.listens_for(His.__table__, "before_drop")
def create_child_tables(target, connection, **kw):
connection.execute("drop table data")
connection.execute("drop table his")
connection.execute("drop sequence his_seq")
e = create_engine('postgresql://localhost:5433/des', echo=True)
#Base.metadata.drop_all(e)
Base.metadata.create_all(e)
s = Session(e)
s.add_all([
Data('hola'),
Data('pedorrete'),
Data('pedorrete2')
])
s.commit()
s.close()
好吧,這個例子(如http://www.sqlalchemy.org/trac/wiki/UsageRecipes/PostgreSQLInheritance中所述 )創建了兩個表,但是sqlalchemy總是使用他的表來插入數據記錄,並將這些表插入到數據和他的數據中。 文本字段(在數據上)確實是在他的表上創建的。
那么,有沒有辦法指定SQLAchemy數據表必須從他繼承(Postgres繼承),並且必須向其添加文本字段,並且當我在數據上插入任何記錄時必須使用數據而不是他的數據?
問候。
SQLAlchemy試圖盡可能地移植,因此它不支持許多Postgres特有的功能。 以下是SA家伙給出類似問題的答案: http : //www.mail-archive.com/sqlalchemy@googlegroups.com/msg17443.html
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